Add solution #32

Author: JoshCrozier

README.md

@@ -37,6 +37,7 @@
 29|[Divide Two Integers](./0029-divide-two-integers.js)|Medium|
 30|[Substring with Concatenation of All Words](./0030-substring-with-concatenation-of-all-words.js)|Hard|
 31|[Next Permutation](./0031-next-permutation.js)|Medium|
+32|[Longest Valid Parentheses](./0032-longest-valid-parentheses.js)|Hard|
 33|[Search in Rotated Sorted Array](./0033-search-in-rotated-sorted-array.js)|Medium|
 34|[Find First and Last Position of Element in Sorted Array](./0034-find-first-and-last-position-of-element-in-sorted-array.js)|Medium|
 35|[Search Insert Position](./0035-search-insert-position.js)|Easy|

solutions/0032-longest-valid-parentheses.js

@@ -0,0 +1,36 @@
+/**
+ * 32. Longest Valid Parentheses
+ * https://leetcode.com/problems/longest-valid-parentheses/
+ * Difficulty: Hard
+ *
+ * Given a string containing just the characters '(' and ')', return the
+ * length of the longest valid (well-formed) parentheses substring.
+ */
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var longestValidParentheses = function(s) {
+  if (!s.length) {
+    return 0;
+  }
+
+  const stack = [-1];
+  let max = 0;
+
+  for (let i = 0; i < s.length; i++) {
+    if (s[i] === '(') {
+      stack.push(i);
+    } else {
+      stack.pop();
+      if (!stack.length) {
+        stack.push(i);
+      } else {
+        max = Math.max(max, i - stack[stack.length - 1]);
+      }
+    }
+  }
+
+  return max;
+};